Imaging devices in the medical diagnostics field, in particular in diagnostic radiology, typically comprise a radiation detector, in particular an X-ray radiation detector, or X-ray detector for short. Imaging devices are generally understood in the present context to mean X-ray machines and specifically computed tomography systems.
X-ray detectors are usually embodied as scintillator detectors or as photon-counting detectors having a direct converter.
Scintillator detectors comprise a scintillator material. Scintillator materials are excited as a result of being irradiated with X-ray radiation and emit the excitation energy in the form of light. The emitted light is subsequently converted, for example via sensor elements embodied as photodiodes, into an electrical sensor signal to produce an output signal, in particular into an electrical current, also known as a signal current, and evaluated in an evaluation unit, the latter usually comprising a plurality of evaluation elements. To that end, each evaluation element usually includes an application-specific integrated circuit (ASIC). The output signal may also have a current pulse, for example, though such current pulses occur only in the case of photon-counting direct converters.
Scintillator detectors frequently comprise a plurality of scintillator elements which are arranged in the manner of an array. Analogously, the sensor elements and the evaluation elements likewise comprise an arrangement in the manner of an array.
Radiation detectors having direct converters usually contain a semiconductor material, for example a semiconductor based on cadmium telluride (CdTe), which converts incident radiation, for example X-ray radiation, into an electrical output signal, in particular into a current pulse.
The two types of detector in each case feature a matrix-like arrangement, both of the sensor elements and of the evaluation elements. In this connection, the sensor elements are also referred to as sensor pixels and the evaluation elements as evaluation pixels.
In order to evaluate the signal currents, a sensor element typically has an electrical connection to an evaluation element associated with it via an electrical interconnect element, for example an electrical line element. The signal currents are typically evaluated in the evaluation unit to produce an output signal and converted, into an image, for example, in a signal processing unit that usually directly follows the evaluation unit.
Because small currents are often evaluated via the evaluation unit and electrical lines typically exhibit parasitic effects, for example parasitic capacitances, the sensor unit and the evaluation unit are frequently embodied as coextensive in area and are arranged one placed on top of the other in order to keep the length of the electrical interconnect elements to a minimum. By small currents, in the present context, are understood electrical currents having a value in the range from 1 pA to 1 μA (per evaluation element). In order to evaluate such small signal currents, each evaluation element typically comprises in addition for example an amplifier unit for amplifying the signal currents and consequently also for amplifying the output signal.
Coextensive embodiment is understood in the present context to mean that the sensor unit and the evaluation unit in each case have a length and a width which each have an equal value, except for a tolerance of <20%, in particular <10%. This applies analogously to the number and distribution of the individual elements (sensor elements and evaluation elements), as well as to a surface area profile, for example in the shape of a rectangle, of the elements (sensor elements and evaluation elements). Furthermore, the sensor unit and the evaluation unit are arranged one on top of the other in a form-fitting manner. This ensures that each sensor element has associated with it an evaluation element which is disposed “opposite” the sensor element. The length of the electrical connection between a sensor element and its associated evaluation element is reduced as a result. In particular, the already mentioned shortest possible electrical connection between the sensor elements and the evaluation elements is guaranteed by this configuration.